24 MILK ANALYSIS 



The reaction should be tested on a drop of the clear liquid, 

 withdrawing it by means of a rod, taking care not to include 

 any solid particles. When the operation is correctly performed, 

 the precipitate, which includes the fat, settles quickly, and car- 

 ries down all of the copper. It is washed by decantation with 

 about 100 c.c. of water, and collected on a filter (previously dried 

 at 130 and- weighed in a weighing bottle). The portions ad- 

 hering to the sides of the beaker are dislodged with the aid of a 

 rubber-tipped rod. The contents of the filter are washed with 

 water until 250 c.c. are collected, which are mixed and reserved 

 for the determination of the sugar as described below. The 

 water in the precipitate is removed by washing once with strong 

 alcohol, and the fat by six or eight washings with ether. An 

 extraction apparatus may be used for this purpose. The wash- 

 ings being received in a weighed flask, the determination of 

 the fat may be made by evaporating the ether, with the usual 

 precautions. 



The residue on the filter, which consists of the proteids in 

 association with copper hydroxid, is washed with absolute 

 alcohol, which renders it more granular, and then dried at 130 

 in the air-bath. It is weighed in a weighing bottle, transferred to 

 a porcelain crucible, incinerated, and the residue again weighed. 

 The weight of the filter and contents, less that of the filter 

 and residue after ignition, gives the weight of the proteids. 

 The results by this method are slightly high, since copper hy- 

 droxid does not become completely converted into copper oxid 

 at 130. 



Richmond & Boseley have modified the process by diluting 

 the milk to 200 c.c., adding a little phenophthalein, and neu- 

 tralizing any acidity by the cautious addition of dilute sodium 

 hydroxid solution, then adding from 2.0 to 2.5 c.c. of the copper 

 sulfate solution. The precipitate is allowed to settle, washed, 

 and estimated as above. 



Casein and Albumin. The most accurate separation of 



